1. Field of the Invention
This invention pertains to that portion of the telecommunications industry having data or voice signals transmitted over optical fibers. More particularly, this invention pertains to attenuators for use in attenuating an optical signal.
2. Description of the Prior Art
In the prior art, attenuators for use in optical fiber systems are well known. Attenuators may be variable (i.e., the amount of the attenuation can be varied by the user) or the attenuators may be fixed (i.e., the amount of the attenuation is fixed and not variable by the user).
There are many methods to making a fixed adaptor type fiber optic attenuator (e.g., by angular misalignment of two optical ends, by longitudinal separation of two optical ends or by inserting a light absorbing filter between two optical ends). However, these methods do not achieve a high return loss.
With attenuators, it is desirable to achieve a high return loss. The term "return loss" in fiber optic components plays a significant role when designing highly sensitive systems and instruments. The purity of the optical signal directly affects systems performance (i.e., bit error rate in digital transmission systems and intermodulation distortion in analog transmission systems). When reflected light is guided back to the transmitting laser, it can alter the longitudinal mode distribution of the emitting laser. Thus, the propagation of the optical power in the fiber can change significantly. These modal changes can not be predicted nor can they be avoided. The designer of a system must prevent any light being reflected back to the laser. High return loss fixed attenuators are very useful in high speed fiber optic systems especially in cable television applications.
To be commercially desirable, a fixed attenuator must be capable of a high return loss. Also, such attenuators should be inexpensive. Furthermore, it is desirable to provide a method of manufacturing an attenuator where the amount of the attenuation can be varied at the time of manufacture such that attenuators of a wide variety of various fixed attenuators can be available through a common manufacturing technique.